WASHINGTON — Members of a Senate subcommittee accused General Motors of trying to cover up problems with an ignition switch that is now tied to 13 deaths, and pressed CEO Mary Barra to commit to punishing anyone involved.

Panel members also told Barra that GM should tell owners to stop driving all the 2.6 million cars being recalled for the faulty switch until they are repaired. GM is currently telling owners that the cars, mainly Chevrolet Cobalts and Saturn Ions, are fine to drive as long as nothing is placed on the key chain.

As she did Tuesday at a House hearing, Barra said many details Congress is seeking will come out in an internal GM investigation that should be completed in 45 to 60 days. She also tried to assure lawmakers that GM is now more focused on safety and the consumer. Many senators were disappointed and not convinced.

“You don’t know anything about anything,” said Barbara Boxer, D-Calif. “If this is the new GM leadership, it’s pretty lacking.”

The questioning from the Senators was more aggressive, with many focused on the ignition switch, namely how GM approved a replacement in 2006 but never changed the part number. Failing to change the part number makes the part harder to track. Anyone investigating the cars wouldn’t know why earlier switches were failing at a higher rate than later ones.

While Barra called the failure to change the part number “unacceptable,” several members of the panel implied that it was done intentionally by person or group within the company, and raised the possibility the action could constitute a criminal violation.

“I don’t see this as anything but criminal,” insisted Sen. Kelly Ayotte, R-N.H., a former prosecutor.

Sen. Richard Blumenthal, D-Conn., told Barra that the more he hears and sees about GM, “the more convinced I am that GM has a real exposure to criminal liability. I think it’s likely and appropriate that GM will face prosecution.”

The Justice Department is conducting a criminal investigation of GM’s handling of the recall. Barra promised the company will cooperate with the probe.

Barra said the company has not yet fired any employees in connection with the recall. But she said if inappropriate decisions were made, GM will take action, including terminating those involved.

As she began her testimony, Barra faced an angry and skeptical Sen. Claire McCaskill, D-Mo., the head of the subcommittee, who recounted the story of a woman who died in an accident involving a faulty switch.

McCaskill said GM had “a corporate culture that chose to conceal rather than disclose.”

McCaskill also dismissed Barra’s claim that there is a new culture at GM. She said that emerging from bankruptcy in 2009, GM had ample time to recall cars equipped with the faulty ignition switch.

GM only began recalling the cars in February.

Blumenthal, who has already submitted a bill that would require the government to make accident reports public, said GM should immediately tell drivers who own the recalled cars not to drive them until they’re repaired because they’re unsafe.

GM has said the ignition switch can move from the “run” position to the “accessory” position because of weight on the key chain. That causes the engine to stall, cutting off power-steering and power brakes, and deactivating the front air bags. GM plans to begin repairing the cars this month, but has said it might take until October to get them all fixed.

Barra said GM has already provided 13,000 loaner cars to drivers who are concerned. But she also said that the company’s testing, on different road surfaces, shows the cars are safe as long as there is nothing but the key on the key chain.

“I would allow my son and daughter — well, my son, because he’s the only one eligible to drive — if he only had the ignition key,” she said.

The acting head of the National Highway Traffic Safety Administration, which oversees auto safety, is also testifying at the hearing.